I'm very sorry to hear that has happened. It sounds like you may have put it into PIP mode. In order for me to help you most accurately, please provide the complete model code for this device. Also, make sure you're on the most recent firmware.
Just purchased a new Samsung Smart TV and I am having a real pain of a issue.
When the tv is on the picture is very tiny and only takes up maybe 1/8th of the screen, in the top right hand corner. The rest of the screen is black. Changing picture size only affects the size of the small picture, I cant seem to make the picture fill the entire screen.